Canadian Journal of Chemical Engineering, Vol.89, No.5, 1029-1039, 2011
MICROMIXING IN TWO-PHASE (G-L AND S-L) SYSTEMS IN A STIRRED VESSEL
The literature on micromixing and local-specific energy dissipation rate, epsilon(T) (on which it depends), for two-phase systems is limited and conflicting. Here, the competitive iodide/iodate reaction scheme has been used to study the effect of particles and gas flow rate on micromixing in a Rushton turbine agitated vessel. Gassing rates up to 1.5 vvm did not show any effect on product distribution compared to the ungassed at constant mean-specific energy dissipation rate (((epsilon) over bar (T))(g) = (epsilon) over bar (T)) for a feeding near the impeller. Near the upper liquid surface, micromixing improved with increasing flow rate because it increased fluid turbulence. These results confirm the limited literature. With 500 mu m glass beads at concentrations up to 2.5 wt.%, micromixing was unaffected near the impeller and near the surface. The related literature is very unclear and it is difficult to draw any precise conclusions. At similar to 12 wt.% when cloud formation was observed, micromixing was significantly worse, especially, it is shown for the first time, in the clear layer above the cloud. The latter finding is significant for processes such as precipitation where micromixing determines the particle characteristics.